The products of genes ntrA, ntrB, and ntrC appear to mediate nitrogen regulation of gene transcription in S. typhimurium. Goals for this grant year are to determine whether the ntrB and ntrC products function as a protein complex and to demonstrate regulation of glnA expression by these products in a coupled in vitro transcription-translation system. An additional goal is to isolate a fusion of the glnA operator-promoter to lacZ which can be used as a template for in vitro protein synthesis. Ability to assay beta-galactosidase rather than glutamine synthetase as a measure of function of the glnA operator-promoter will simplify attempts to demonstrate regulatory effects of ntr gene products in vitro.